1. Field of the Invention
The present invention relates to a method for producing a semiconductor light emitting device, and specifically a method for producing a semiconductor light emitting device including a nitride semiconductor layer as a light emitting layer on a silicon substrate; and a semiconductor light emitting device produced by such a method.
2. Description of the Related Art
A light emitting device using a nitride semiconductor material, such as GaN, InN, AlN, or a mixed crystal thereof, usually includes a nitride semiconductor layer formed of, for example, InxGa1-xN crystals, as a light emitting layer on a sapphire substrate.
Recently, silicon (Si) substrates which are less expensive and have a larger area than a sapphire substrate have been produced. A nitride semiconductor light emitting device can be produced at lower cost by using such an Si substrate instead of a sapphire substrate.
A nitride semiconductor light emitting device produced using an Si substrate has the following problem. A nitride semiconductor layer has a larger thermal expansion coefficient than that of an Si substrate. When the temperature is once raised for epitaxial growth and then is lowered to room temperature, the nitride semiconductor layer shrinks more significantly than the Si substrate, due to the difference in the thermal expansion coefficient between the Si substrate and the nitride semiconductor layer.
FIG. 12 is a schematic perspective view of a nitride semiconductor light emitting device 500 using an Si substrate 91. As shown in FIG. 12, when the temperature is raised to form a nitride semiconductor layer 92 on the Si substrate 91 by epitaxial growth and then lowered to room temperature, the nitride semiconductor layer 92 significantly shrinks. As a result, tensile stress is applied to an interface between the Si substrate 91 and the nitride semiconductor layer 92, thus possibly causing cracks 93.
In the case of a nitride semiconductor light emitting device having a double-hetero structure, when the cracks 93 are generated, an invalid leak current which does not contribute to light emission is increased in magnitude. This prevents output of high luminance emission. In order to produce a nitride semiconductor device having a long life and high luminance emission, it is indispensable to prevent the generation of such cracks 93.
FIG. 13 is a schematic cross-sectional view illustrating a production step of another conventional semiconductor light emitting device 600.
The semiconductor light emitting device 600 is produced as follows. A mask layer 41B having openings (windows) 42B is formed on an Si substrate 91A using an oxide layer or the like, and then a nitride semiconductor layer 92A is formed in each of the openings 42B of the mask layer 41B by epitaxial growth. Owing to such a step, a tensile stress applied to an interface between the Si substrate 91A and the nitride semiconductor layer 92A is alleviated, thus preventing the generation of cracks.
This method has the following problem. Depending on the size of the mask layer 41B, the width and material of the mask layer 41B, and the growth temperature and rate, the material used for the epitaxial growth remains on the mask layer 41B. This raises the concentration of the material in a peripheral portion of the nitride semiconductor layer 92A in the opening 42B, which is in the vicinity of the mask layer 41B, is excessively high. As a result, as shown in FIG. 13, the peripheral portion of the nitride semiconductor layer 92A in the opening 42B is about three times as thick as a central portion thereof, due to growth referred to as xe2x80x9cedge growthxe2x80x9d. Such a thick peripheral portion is subjected to significant local distortion, and as such is susceptible to being cracked.
As described above, the method of forming the nitride semiconductor layer 92A by epitaxial growth in the opening 42B prevents the central portion thereof from being cracked, but has a risk of causing cracks in the peripheral portion of the nitride semiconductor layer 92A due to the local distortion applied to the thick portion.
When a substrate formed of a material having a smaller thermal expansion coefficient than a nitride semiconductor material, such as Si, it is difficult to produce a nitride semiconductor light emitting device having a long life and high luminance emission, with prevention of crack generation. It is not sufficient to form a nitride semiconductor layer in an opening by epitaxial growth.
According to one aspect of the invention, a method for producing a semiconductor light emitting device includes the steps of forming a mask layer having a plurality of openings on a surface of a silicon substrate; and forming a column-like multi-layer structure including a light emitting layer in each of the plurality of openings with nitride semiconductor materials. A width between two adjacent openings of the plurality of openings of the mask layer is 10 xcexcm or less.
According to another aspect of the invention, a method for producing a semiconductor light emitting device includes the steps of forming a mask layer having a plurality of openings on a surface of a silicon substrate; and forming a column-like multi-layer structure including a light emitting layer in each of the plurality of openings with nitride semiconductor materials. A width between two adjacent openings of the plurality of openings of the mask layer is in the range of twice a thickness of the column-like multi-layer structure to 40 xcexcm, the thickness being in a direction vertical to the planar direction of the silicon substrate.
In one embodiment of the invention, the method for producing a semiconductor light emitting device further includes the steps of removing the mask layer and providing an insulating layer for electrically insulating the column-like multi-layer structures from each other on an area of the surface of the silicon substrate from which the mask layer has been removed, and forming a transparent electrode for electrically connecting the column-like multi-layer structures to each other.
In one embodiment of the invention, the method for producing a semiconductor light emitting device further includes the steps of forming a transparent electrode on each column-like multi-layer structure; and dividing an assembly of the silicon substrate and the column-like multi-layer structures into a plurality of chips, such that each chip includes one column-like multi-layer structure.
In one embodiment of the invention, the plurality of openings are each square or rectangular. The plurality of openings each have a side in the range of 50 xcexcm to 150 xcexcm.
In one embodiment of the invention, the plurality of openings are each square or rectangular. The plurality of openings each have a side in the range of 200 xcexcm to 300 xcexcm.
In one embodiment of the invention, each column-like multi-layer structure includes a hexagonal-system gallium nitride-based compound semiconductor material. The plurality of openings are polygonal. At least one side of each polygonal opening is parallel to a  less than 11-20 greater than  axis of the gallium nitride-based compound semiconductor material.
In one embodiment of the invention, the silicon substrate has an Si (111) plane. A  less than 1-10 greater than  axis of the silicon substrate is parallel to the  less than 11-20 greater than  axis of the gallium nitride-based compound semiconductor material.
In one embodiment of the invention, the mask layer is formed of a material selected from the group consisting of silicon oxide, silicon nitride, and aluminum oxide.
According to still another aspect of the invention, a semiconductor light emitting device produced by the above-described.
Thus, the invention described herein makes possible the advantages of providing a method for producing a semiconductor light emitting device using an Si substrate and still preventing cracks from being generated at an interface between the Si substrate and a nitride semiconductor layer; and a semiconductor light emitting device produced by such a method.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.